1. Field of the Invention
The present invention relates to an optical modulation device, and more particularly to a liquid crystal-optical shutter. Specifically, the present invention relates to a liquid crystal-optical shutter suitable for a time-sharing driving method.
2. Description of the Prior Art
Liquid crystal-optical shutters utilize the electro-optical modulation function of liquid crystals, wherein light is irradiated to modulation cells arranged in the form of an array, thereby to form optical signals corresponding to electrical image signals by selectively outputting transmitted light therethrough. These optical signals are irradiated to e.g. a photosensitive member to obtain a digital copy.
Advantages obtained with a liquid crystal-optical shutter array are as follows.
(1) When applied to an electrophotographic printer, the printer becomes small in apparatus size.
(2) There is no mechanically movable parts such as a polygon scanner used in an LBP (Laser Beam Printer), resulting in no noise and little requirement for strict mechanical precision.
The fact that a liquid crystal shutter array can offer these advantages leads to the possibility of improved reliability, light weight and reduced cost. However, there practically exist various difficulties.
Referring to FIG. 1, there is shown an example of a crystal shutter array which would be most easily understood.
As shown in FIG. 1, there are provided openings 11 of the shutter, and the remaining parts except for openings are usually masked so that leakage light is not produced. Liquid crystals are hermetically disposed between signal electrodes 13 (13a, 13b, 13c, 13d . . . ) provided at the inner wall surface of an electrode plate 12 and common electrodes 14 disposed opposite to signal electrodes 13. Lead wires 15 and a lead wire 16 are drawn out from electrodes 12 and 13, respectively, and are connected to a shutter array driving circuit (not shown).
However, if the openings are aligned in a manner shown in FIG. 1 and an attempt is made to design a shutter array having a denisty of the picture elements for forming images of 10 dots/mm and a length corresponding to the width of paper size A4, about 2,000 signal electrodes are required. Accordingly, about 2,000 drivers each required for driving a signal electrode are required.
This means that 40 integrated circuit (IC) chips for drivers are required when IC chips each having 50 pins are used, giving rise to serious obstacle to reduction in cost.
For this reason, another attempt is proposed to divide a common electrode into a plurality of row electrodes. Thus, the plurality of row electrodes are so arranged as to form a matrix in combination with signal electrodes. With respect to each row of the common electrode, the opening and closing operation of a shutter is effected by making use of a time-sharing method. However, when using such a liquid crystal shutter array, there is a possibility that light is transmitted not only through a shutter of the row electrode at which the opening and closing operation of the shutter is effected, but also through another shutter of row electrodes placed in shutter off condition, thus failing to obtain high performance. Particularly, the gaps formed between the common electrodes on the common electrode plate for driving a liquid crystal shutter in a time-sharing manner cause a drawback in structural point of view that light leaks therethrough.